The invention relates to a capped electric lamp which includes
a lamp vessel having a first and a second mutually opposing neck-shaped portions with seals through which a first and a second current supply conductor, respectively, extend to an electric element arranged in the lamp vessel;
a metal clamping member which clamps around the first neck-shaped portion of the lamp vessel;
a metal fixation member provided with first tongues which are connected to the clamping member;
a lamp cap of insulating material connected to the lamp vessel and having at a side facing the lamp vessel a first, circumferential cavity in which the fixation member is fixed and a second, central cavity in which the first neck-shaped portion is accommodated, which central cavity affords access to a side of the lamp cap facing away from the lamp vessel where the tamp cap supports a first and a second contact member to which the first and the second current supply conductor, respectively, are connected,
the lamp cap at its side facing the lamp vessel having an opening providing access to the side facing away from the lamp vessel, separated from the second cavity, through which opening a connection conductor extends from the second contact member alongside the lamp vessel to the second current supply conductor.
The invention also relates to a connector for this lamp.
Such a lamp in which the electric element is a pair of electrodes is described in the not previously published European Patent Application 91.202.390, now U.S. Pat. No. 5,216,319 (Van Heeswijk). The lamp is designed for use as a vehicle headlamp.
To render it possible to ignite such a lamp while it is still hot, not only a high voltage of several kV is used, but also a high frequency of several kHz.
Owing to its high brightness, the lamp renders it possible to use a headlight of very small height, for example 5 cm. If the lamp is to be accommodated therein, however, it must be of a compact construction.
In the electric discharge lamp described in the said Patent Application, the fixation member does not pass current. However, insulated cables issue from the lamp cap to the exterior, which cables may be connected to a supply source by means of, for example, welding. A disadvantage of this is that a defective lamp cannot be replaced without tools.
EP 0.309.041 A discloses a high-pressure discharge lamp of the kind described in the opening paragraph destined for use as a vehicle headlamp, in which the fixation member passes current. The lamp cap is provided with contact pins in an asymmetrical configuration.
The compact construction of the lamp known from said EP 0.309.041 and the high voltages applied with their high frequencies may cause damaging and disadvantageous electrical effects, such as corona discharges, owing to which the voltage across the lamp can drop and materials of the lamp can be attacked. As a result, breakdown may occur in the course of time. These effects do not occur at low frequencies, for example below 100 Hz, with the other voltage and geometry conditions remaining the same.
The known lamp can be replaced without tools in case of a defect, but it is difficult to provide a connector. Often there is little room behind the headlights in vehicles, and it is difficult to see in what position the connector is to be provided on an inserted lamp.